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Did An Icy Collision Produce The Odd Shape Of Asteroid 624 Hektor?

Artist's impression of 624 Hektor, the largest known Trojan asteroid. The dual asteroid is 155 miles (250 kilometers) at its widest. It also has a 7.5-mile (12-mile) moon. Credit: H. Marchis/F. Marchis

Artist’s impression of 624 Hektor, the largest known Trojan asteroid. The dual asteroid is 155 miles (250 kilometers) at its widest. It also has a 7.5-mile (12-mile) moon. Credit: H. Marchis/F. Marchis

Two icy asteroids could have crashed into each other early in the solar system’s history to form the strange-looking 624 Hektor, new research reveals. The 155-mile (250-kilometer) asteroid is the largest known Trojan asteroid, or space rock that follows along with Jupiter in the gas giant’s orbital path.

Hektor also has a moon, which was first discovered in 2006 by another team led by the same lead author, the SETI Institute’s Franck Marchis. It’s taken the astronomers about eight years to get a handle on the complex orbit of the system, a topic that the new research examines in detail. That was partly because the path was so “bizarre”, the team stated, and also because time on the W.M. Keck Observatory telescopes (used to perform the observations) is limited. There are few other observatories that could do the same work, the team added.

The moon, which is about 7.5 miles or 12 kilometers in diameter, orbits its parent asteroid every three days. The moon’s path is about 373 miles (600 km) distant and inclined almost at 45 degrees to the asteroid’s equator.

The Trojan asteroid 624 Hektor is visible in these two adaptive optics observations in July 2006 and October 2008, both performed with the W.M. Keck Observatory's II telescope. Hektor is in the middle of each picture, and its moon in the circles. Credit: WMKO/Marchis

The Trojan asteroid 624 Hektor is visible in these two adaptive optics observations in July 2006 and October 2008, both performed with the W.M. Keck Observatory’s II telescope. Hektor is in the middle of each picture, and its moon in the circles. Credit: WMKO/Marchis

“The orbit of the moon is elliptical and tilted relative to the spin of Hektor, which is very different from other asteroids with satellites seen in the main-belt,” stated Matija Cuk, a paper co-author who is a scientist at the Carl Sagan Center of the SETI Institute. “However, we did computer simulations, which include Hektor being a spinning football shape asteroid and orbiting the Sun, and we found that the moon’s orbit is stable over billions of years.”

While the artist’s conception above shows Hektor as a peanut, the exact shape is still not known for sure. The models and the adaptive optics suggest that it is likely a dual-lobe asteroid. What is better known, however, is that the asteroid is “extremely elongated” and spins in less than seven hours.

The origin of the moon is unclear, but the researchers suggested it could be because of ejecta associated with the collision that formed the asteroid. They said more simulations are needed on that point. What’s more, Hektor has another mystery associated with its composition.

An artist's rendering of a Kuiper Belt object. Image: NASA

An artist’s rendering of a Kuiper Belt object. Image: NASA

“We also show that Hektor could be made of a mixture of rock and ices, similar to the composition of Kuiper belt objects, Triton and Pluto. How Hektor became a Trojan asteroid, located at only 5 times the Earth–Sun distance, is probably related to the large scale reshuffling that occurred when the giant planets were still migrating,” stated Julie Castillo-Rogez, a researcher at NASA’s Jet Propulsion Laboratory who participated in the research.

You can read more about the research in Astrophysical Journal Letters. By the way, the moon does not have a name yet, and the researchers said they are looking for any ideas as long as it fulfills a couple of ideas: “the satellite should receive a name closely related to the name of the primary and reflecting the relative sizes between these objects.” Feel free to share your suggestions in the comments.

Source: W.M. Keck Observatory

About 

Elizabeth Howell is the senior writer at Universe Today. She also works for Space.com, Space Exploration Network, the NASA Lunar Science Institute, NASA Astrobiology Magazine and LiveScience, among others. Career highlights include watching three shuttle launches, and going on a two-week simulated Mars expedition in rural Utah. You can follow her on Twitter @howellspace or contact her at her website.

Comments on this entry are closed.

  • Stickmaker February 28, 2014, 11:53 AM

    Don’tcha’ just love inelastic collisions? ;-)

    I’m wondering how they know it’s that old. However old it is, it hasn’t come close to any substantial body – Jupiter being the most substantial of our planets – or tidal forces would have torn that apart.

    Now I’m remembering a juvenile SF novel I read as a kid, where they find an ancient alien spacecraft partially embedded in a lightly consolidated asteroid.

    • Aqua4U February 28, 2014, 8:54 PM

      Your interstellar craft collects hydrogen and oxygen molecules in it’s wake field. Those particles are collected and used to make a water ice shell around the craft. This protects if from radiation and meteor strike on it’s long voyage. The water ice shell weighs nothing initially and is easily shed at the end of the voyage, making deceleration easier with less mass……

  • om sam February 28, 2014, 11:54 AM

    Here’s one. Skamandrios. He’s the infant son of the Hektor from the Iliad.

  • Gozlemci March 1, 2014, 8:15 AM

    It seems, it may be caused by something like “soft contact” rather than “collision”…

    • eSpace March 1, 2014, 8:57 PM

      Yes, and it doesn’t appear that this is really an “odd” shape for spacerocks, either. See pics of comets Borrelly, Halley, and Elenin as well as asteroids 9969 Braille and Itokawa. Think I just saw a report that the two lobes of Itokawa have different compositions. On Itokawa, it’s easy to visualize to bodies locked together with a connecting bridge formed by dust settling at the center of gravity and showing a smoother texture.

  • jc hanford March 3, 2014, 8:41 AM

    A preprint of “The Puzzling Mutual Orbit of the Binary Trojan Asteroid (624) Hektor” is available here: http://arxiv.org/abs/1402.7336

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